The application of low-bicarbonate or bicarbonate-free autoclaved and chemically defined culture media, now in use for several primary and long-term culture systems, will be extended to other cells and organs of the mouse. The media will be adapted to each cell or tissue type by adjustment of pH, cation balance, osmolality, hormone content, or other cell or tissue specific requirements. A ssufficient postnatal mouse liver cells in established culture become available, their characteristics will be examined and compared with those of the already characterized cells derived from mouse fetal livers. In particular, the hormonal control of serum protein production will be studied in these cells. Attempts will be made to place the differentiated functions of other cell types (e.g., lung, prostate, kidney, and heart) under experimental control by manipulation of the chemically and physically defined environment.